The present invention relates to a method of and an apparatus for feeding and tightening a band in a band strapping machine. Particularly, it relates to a method of feeding a band around a package and giving to the band primary and secondary tightening operations by means of a feed roller rotated in one direction, a return roller disposed in parallel to the feed roller and rotated in the opposite direction and rocker rollers each adapted to come in press-contact with the feed roller and the return roller.
FIG. 1 is a schematic view of a conventional band strapping machine of this type, FIG. 2 is an enlarged front view of a band feeding and tightening apparatus contained in the conventional strapping machine and FIG. 3 is a plan view showing an arrangement of and connection between a feed roller and a return roller of the conventional strapping machine.
In FIGS. 1 to 3, a reference numeral 5 designates a motor placed in the strapping machine body 1. A belt 6 is extended from a shaft of the motor 5 to be wound around a pulley 8 and a pulley of a reduction gear device 7. The pulley 8 is attached to one end of a feed shaft 12. A feed roller 11 is attached to the other end of the shaft 12 and a gear wheel 18 is attached to the intermediate portion of the shaft 12. The feed shaft 12 is supported by a machine frame (not shown) in a freely rotatable manner. A return shaft 15 is provided in parallel to the feed shaft 12. A return roller 13 is attached to an end portion of the return shaft 15 at a position corresponding to the feed roller 11. At the intermediate portion of the return shaft 15, a gear wheel 17 meshing with the gear wheel 18 of the feed shaft 12 is attached through a clutch 16, whereby the return shaft 15 is rotated in the direction opposite to the feed shaft 12. The construction of the clutch 16 is such that it transmits rotation of the feed shaft 12 to the return shaft 15 through the gear wheels 17, 18, and when a load of a predetermined level or greater is applied to the return shaft 15 through the return roller 13, the return shaft 15 is stopped from rotating due to slippage of the clutch 16. The sprocket 14 provided with a clutch therein is provided on the return shaft at a position opposite the return roller 13. A chain 62 is extended between the sprocket 14 and a sprocket body 19 of the reduction gear device 7. By this transmission mechanism, a torque is not transmitted from the return shaft 15 to the sprocket 14, and a rotation of the sprocket body 19 of the reduction gear device 7 causes a rotation of the return shaft 15 in the clockwise direction (the direction indicated by an arrow mark in FIG. 3) by means of the chain 62 and the sprocket 14.
In FIG. 2, above and below the feed roller 11, rocker rollers 30, 31 are respectively pivoted at the top ends of L-shaped levers 32, 33. The bent portion of each of the L-shaped lever is pivoted by a pin 34 or 35. The other end of the lever 32 is connected to an end of the operating rod of an solenoid 42. The other end of the lever 33 is linked to the intermediate portion of the lever 32 by means of a rod 36. A compression spring 37 is fitted between a nut fastened at the other end of the rod 36 and the other end of the L-shaped lever 33.
Below the return roller 13, a rocker roller 40 is pivotally supported at the intermediate portion of a lever 39, whose one end is pivotally supported by the pin 35 and whose other end is connected to an end of an operating rod of a solenoid 41.
The band 4 is passed from the lower part of the feed roller 11 to a space between the feed roller 11 and the rocker roller 31 and a space between the return roller 13 and the rocker roller 40 in this order, and then passed around the return roller 13 by the aid of a band guide 43 and thereafter, passed between the feed roller 11 and the rocker roller 30 and finally, passed into an arch guide 2 set up on a table for packaging (not shown). A reference numeral 3 designates a cam mechanism for clamping, melt bonding and cutting the band wound around a package.
The operation of the conventional band strapping machine will be described.
When the solenoid 42 is actuated, the rocker rollers 30, 31 are brought into press-contact with the outer circumferential surface of the feed roller 11 to feed the band in the arch guide 2. Then, as soon as the solenoid 42 is deenergized, the solenoid 41 is actuated to bring the rocker roller 40 into press-contact with the circumferential surface of the return roller 13 to thereby perform the primary tightening operation for the band. When a tightening force reaches a predetermined value, slippage is caused in the clutch 16 interposed between the return roller 13 and the return shaft 15. Accordingly, revolution speed of the return shaft 15 rapidly decreases. In this case, a rotational force of a low speed and a high torque from the reduction gear device 7 is transmitted to the return shaft 15 by means of the chain 62 and the sprocket 14. Thus, a strong secondary tightening operation is given to the band.
The conventional method and apparatus have encountered the following disadvantage. Namely, when change is made from the primary tightening operation i.e. a high speed operation to the secondary tightening operation, i.e. a low speed operation, there takes place a shock at the time of completion of the primary tightening operation which is caused by structural elements of the strapping machine having large mass, such as the return roller 13, the return shaft 15 and the friction clutch (the follower part) provided on the return shaft. The shock is added to the primary tightening operation. Accordingly, when a solid article such as a wooden box is packaged, fairly large noise is generated due to the shock. When a carton box which is weaker than a wooden box is packaged, it is sometimes broken.
In the conventional strapping machine, the return roller is rotated at a high speed when the feed roller performs feeding of the band at a high speed. Accordingly, when timing in the band feeding operations is not properly adjusted, a trouble of contact takes place between the band and the return roller, particularly the return roller becomes worn after a short term and is damaged by heat of friction.